1. Field of the Invention
The present invention relates to a center take-off type hydraulic power steering apparatus. More particularly to a center take-off type hydraulic power steering apparatus which intends to protect a dust boot covering a portion in which one end of a rack shaft, commonly serving as a power piston rod, passes through a power cylinder so as to protrude in a direction of a wheel house.
2. Description of Related Art
Conventionally, in most of the center take-off type hydraulic power steering apparatus, a design is made so that a range of a stroke of the rack shaft commonly serving as the power piston rod is received within a power cylinder housing. However, in accordance with the structure mentioned above, a difference is generated between right and left pressure receiving areas of the power piston within the power cylinder chamber and unbalance is generated between right and left power assist characteristics. In order to remove the unbalance so as to make the right and left power assist characteristics equal, it is unavoidable that a structure of a gear box portion becomes complex.
In order to avoid a complex structure of the gear box portion, there has been developed a structure such that one end of the rack shaft passes through the power cylinder so as to protrude in a direction of a wheel house. This makes the right and left pressure receiving areas of the power piston equal to each other, whereby the right and left power assist characteristics are made equal to each other.
In this structure, the size of the apparatus is increased when covering the portion in which one end of the rack shaft protrudes from the power cylinder by the housing. Hence the structure is made such that the dust boot is put over the protruding portion, the end portion of the dust boot is fixed to the end portion of the rack shaft and the end portion of the dust boot serves the same motion as that of the end portion of the rack shaft.
However, the end portion of the rack shaft moves within the wheel house so as to reciprocate when fixing the end portion of the dust boot to the end portion of the rack shaft. Therefore snow is attached and frozen on inner and outer surfaces of a wall of a wheel house chamber, the end portion of the rack shaft and the end portion of the dust boot are collided with the snow wall when a vehicle runs on a snow road in winter. This produces a risk that the end portion of the dust boot is damaged. Further, when the end portion of the dust boot is broken in this manner, the water enters into the gear box housing from the breaking portion, thereby causing an inferior operation and a reduction of durability of the power steering apparatus.
An object of the present invention is to provide a center take-off type hydraulic power steering apparatus which can solve the problems mentioned above contained in the conventional center take-off type hydraulic power steering apparatus. Also it is able to prevent a dust boot put over a portion in which one end of a rack shaft commonly serving as a power piston rod passes through a power cylinder so as to protrude in a direction of a wheel house from being broken by a snow wall attached and frozen on inner and outer surfaces of a wall of a wheel house chamber.
In accordance with the present invention, there is provided a center take-off type hydraulic power steering apparatus structured such that respective inner ends of a pair of right and left tie rods are provided so as to be positioned at a substantially center portion of a vehicle body. One end of a rack shaft commonly serving as a power piston rod passes through a power cylinder so as to protrude in a direction of a wheel house. A dust boot disposed between one end of the rack shaft and one end of the power cylinder housing, wherein a boot guard shutting a side opposing to the wheel house of the dust boot is integrally mounted to one end of the rack shaft.